Schools across state won’t reopen before Diwali: Maharashtra Govt. Mumbai: With Covid-19 positive cases showing no signs of slowing down in Maharashtra, the state government has decided to allow schools to reopen only after Diwali. This means children in over 1.2 lakh schools won’t be able to attend classes in person till November. Minister of School Education Varsha Gaikwad said the decision was taken after a meeting between her department and several school managements. Since schools are not ready to risk the lives of their students, the state has planned to push the reopening after Diwali, she said. Gaikwad said the Centre had sought the state government’s views about the resuming classes in schools for senior students. She said the Centre had also issued standard operating procedures or SOPs for the partial resumption of teaching activities in schools for students of Classes 9 to 12, on a voluntary basis, from September 21. Advertisement Advertisement “However, school managem...
1. Solid state.
(Primitive/simple cubic unit cell):-
-Has particles at its eight corners.
-Each corner particle share's it's all seven parts to other unit cell to form crystal.
-so, only 8th part comes under crystal.
-So, 1/8×8 ( corner ) = 1 particle per unit cell.
Body-centred cubic unit cell :-
-In bcc unit cell,
-[1/8th (part of single unit corner) × 8 + 1 × particle at body ] = 2 ( particles )
Face-centred cubic unit cell :-
-In FCC,
-[1/8th (given unit cell at corner)× 8 + (1/2×6 face)]
- [1+3]
- 4 particle.
Packing of particle in crystal lattice :-
- Particles are closed packed in crystalline solid.
- Always individual particle is treated as hard sphere.
- The number of neighbouring spheres that touch any given sphere is its coordination number.
-Magnitude of coordination number is measure of compactness of solid.
- Larger the coordination number, the closer are the sphere to each other.
1) Close packed structure :-
-It may one dimension or two dimension close packing.
-One dimensional results in arranging the sphere to touch each other in raw.
-Two-D is nothing but planar structure.
-It is nothing but stacking of raw to from structure.
(I) Square close packing :-
- Coordination no is 4.
- i.e Each sphere is touched with 4 spheres.
- All the raws are of the same type.
-Example - A.A.A ___ type.
(2) Hexagonal close packing :-
-Coordination no is 6.
-i.e Each sphere is touched with 6 spheres.
-Each raw are of different types.
-AB.AB.AB ____ type.
(3) Close packing in 3-D :-
- Stacking of 2-d layers gives rise to 3-d crystal structure.
Stacking of Square close packed layer :-
- Stacking of Square closed packed layer generate a 3-d simple cubic structure.
- All arrangement of layer is described as AAA __ type.
-Example : pollonium-- is only metal that crystallize in simple cubic closed packed structure.
Stacking of two hexagonal close packed layers :-
-Hexagonal closed packed structure are arranged in particular manner to create this.
-Sphere of 2nd layer is placed in depperession of 1st layer.
- If 1st layer is A.
- Then 2nd layer is B.
Placing third hexagonal closed packed layer :-
- There are two types - I) One way.
II) The second way.
I) one way :-
- Is to align the spheres of the third layer with the sphere of first layer.
-This arrangement results in hexagonal close packed structure
II) second way :-
- pattern of checking exact or null close packed layers is called ABCABC....
- This arrangement results in cubic close packed.
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